This invention relates to articles comprising a base coated with a pressure-sensitive silicone adhesive and a releasable anti-stick layer on the adhesive, and to a method of employing the article.
ORGANOPOLYSILOXANE COMPOSITIONS HAVE BEEN WIDELY USED AS PRESSURE-SENSITIVE ADHESIVES. When various silicone resins and gums are mixed, interreacted or intercondensed and applied to suitable substrates or backings there are provided pressure-sensitive adhesive articles. The adhesives can be formulated to serve over broad temperature ranges, such as from about -50.degree. C. to about 250.degree. C., and will retain their tack and cohesion over these ranges, while exhibiting a low level of moisture sensitivity. In addition, organopolysiloxane pressure-sensitive adhesives have excellent electrical properties. Finally, organopolysiloxane pressure-sensitive adhesives exhibit outstanding adhesive characteristics on a wide variety of substrates. They are suitable for many substrates for which non-silicone pressure-sensitive adhesives have shown little or no affinity, such as for "Teflon" substrates.
After preparation and before use, articles having a pressure-sensitive adhesive layer require that the surface of the layer be protected both from contamination and from adhering or sticking to undesired surfaces. In addition, if such an article is to be used in the form of a tape and wound in rolls, the backing of one layer will necessarily come into contact with the pressure-sensitive adhesive coating on the layer thereabove. This contact will often cause the upper layer to adhere to the next lower layer, making it extremely difficult to unwind the tape because of the aggressively tacky characteristic of the organopolysiloxane pressure-sensitive adhesive.
For these reaons, it is necessary to employ a protective, releasable film or coating adjacent the pressure-sensitive adhesive.
One of the best known of such release coatings is a cured composition based on a silanol-stopped, dimethylpolysiloxane fluid, e.g., General Electric Co. SS-4191. This is coated onto a release paper sheet and then applied to the pressure-sensitive adhesive. Other good release coatings include cured compositions based on dimethylvinyl-stopped dimethyl polysiloxane fluid, e.g., General Electric Co. SS-4280, and dimethylhydrogen-stopped dimethylpolysiloxane fluids.
However, with conventional adhesives, e.g., one based on a silanol-stopped dimethyl gum, the peel strength between the adhesive and the release sheet is sufficiently high that often the paper sheet tends to tear frequently when stripped. The peel strength immediately after laminating is high, and of the order of 25 oz./in.
It has now been discovered that if a particular type of adhesive is selected, namely, one in which the gum component differs from the conventional adhesive mentioned above, in that it uses at least one copolymer gum containing diphenylsiloxane units and especially preferably, methyl vinyl siloxane units and vinyl chainstoppers, as well, a vast decrease in peel strength between the reactive end group containing methylpolysiloxane fluid-coated release paper and the adhesive coated backing is obtained. This is of the order of 4 oz./in. and paper tearing is eliminated. The easy release capabilities are retained even after accelerated oven aging and the subsequent adhesion of such tapes, e.g., after application to stainless steel test panels, is excellent over prolonged periods of oven aging.